The battery is a fundamental component of electric vehicles, which represent a step forward towards sustainable mobility. Lithium chemistry is now acknowledged as the technology of choice for energy storage in electric vehicles. However, several research points are still open. They include the best choice of the cell materials and the development of electronic circuits and algorithms for a more effective battery utilization. This paper initially reviews the most interesting modeling approaches for predicting the battery performance and discusses the demanding requirements and standards that apply to ICs and systems for battery management. Then, a general and flexible architecture for battery management implementation and the main techniques for state-of-charge estimation and charge balancing are reported. Finally, we describe the design and implementation of an innovative BMS, which incorporates an almost fully-integrated active charge equalizer
A simple but effective analysis to calculate the performances achievable by a balancing circuit for series-connected lithium-ion batteries (i.e., the time required to equalise the battery and the energy lost during this process) is described in this paper. Starting from the simple passive technique, in which extra energy is dissipated on a shunt resistor, active techniques, aiming at an efficient energy transfer between battery cells, are investigated. The basic idea is to consider the balancing circuit as a DC/DC converter capable of transferring energy between its input and output with a certain efficiency and speed. As the input and output of the converter can be either a single cell or the entire battery pack, four main active topologies are identified: cell to cell, cell to pack, pack to cell and cell to/from pack (i.e., the combination of the cell to pack and pack to cell topologies when the converter is bidirectional). The different topologies are compared by means of statistical simulations. They clearly show that the cell to cell topology is the quickest and most efficient one. Moreover, the pack to cell topology is the least effective one and surprisingly dissipates more energy than the passive technique, if the converter efficiency is below 50 %.
We experimentally investigate the benefits of a new optical pulse coding technique for long-range, meter and submeter scale Raman-based distributed temperature sensing on standard single-mode optical fibers. The proposed scheme combines a low-repetition-rate quasi-periodic pulse coding technique with the use of standard high-power fiber lasers operating at 1550 nm, allowing for what we believe is the first long-range distributed temperature measurement over single-mode fibers (SMFs). We have achieved 1 m spatial resolution over 26 km of SMF, attaining 3°C temperature resolution within 30 s measurement time. © 2011 Optical Society of America OCIS codes: 060.2370, 280.1350 Distributed fiber-optic sensors based on Raman scattering are becoming a widely adopted technology [1], with a range of industrial applications spanning from oil and gas pipelines (for fire and leakage detection), to firealarm systems, reservoir and power cables monitoring. Raman-based distributed temperature sensor (RDTS) systems exploit the strong temperature sensitivity of the anti-Stokes Raman backscattered light, which is, however, characterized by extremely low power values, resulting in challenging measurements and requiring the use of high-sensitivity photodiodes, as well as the acquisition of many traces to decrease the noise impact through averaging. To partially overcome the trade-off among temperature resolution, sensing range and acquisition times, RDTS systems commonly employ multimode fibers (MMFs) [2,3], which are characterized by higher backscattering coefficients and also allow for higher input peak power levels before the onset of nonlinearities [3]. Unfortunately, modal dispersion ultimately limits the RDTS spatial resolution when using MMFs. Although this issue can be partially overcome by using graded-index MMFs, the best achievable spatial resolution is still limited to several meters when operating over long sensing ranges (tens of kilometers). In spite of these limitations, for many applications a better spatial resolution would be highly desired over long distances, together with fast acquisition times and high temperature resolution. In order to enhance the sensing performance of RDTS systems, optical pulse coding techniques have been proposed based on either directly or externally modulated semiconductor lasers in MMFs [2] and SMFs [4]. In both cases the strong potential in terms of signal-to-noise ratio (SNR) enhancement provided by optical coding has been somehow limited by the available power in semiconductor lasers. In particular, for RDTS systems operating on standard SMFs with pulse coding, the maximum peak power level from a semiconductor laser that can be reasonably coupled into the sensing fiber is of the order of few hundred milliwatts; however, in principle, up to ∼3-4 W could be used before exciting detrimental nonlinear effects, such as stimulated Raman scattering.Hence, the use of new coding schemes, which could be used with high-power pulsed lasers [such as Q-switched and rare-earth-doped fiber lasers ...
An accurate model of the elementary accumulation device is fundamental for sizing and controlling the battery pack to be used in electric and hybrid vehicles. Indeed, the implementation of such a model within the Battery Management System makes it possible to evaluate the status and the behavior of the battery pack in every condition and to apply a correct control strategy. This work shows the characterization and modeling of a commercial Lithium-Polymer cell, which properly considers thermal effects on cell behavior. The specific designed thermostatic chamber is described and the experimental results are presented and compared to those simulated with the developed model.
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